I quickly made a test subclass of ActiveMapper called LazyMapper that
let's you delay the actual query until the moment you iterate or slice
the results, just like SQLObjects.
i = Person.select(**you conditions**)
list(i[10:15]) -> issues a select with limit 5 offset 10
To use it:
1. Drop lazymapper.py next to your model.py
2. In model.py add: from lazymapper import LazyMapper
3. Replace the parent in your sqlalchemy objects for LazyMapper:
class Person(ActiveMapper): -> class Person(LazyMapper)
We may need this in the future to complete TG pagination support.
I know this belongs to the SA mailing list (I'll submit this there too),
but I want to see if it works ok on TG apps already using SA.
--
Claudio
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from sqlalchemy.ext.activemapper import ActiveMapperMeta, ActiveMapper
def select(cls, *args, **kw):
return SelectResults(cls, *args, **kw)
select = classmethod(select)
class LazyMapperMeta(ActiveMapperMeta):
def __init__(cls, name, bases, dict):
super(LazyMapperMeta, cls).__init__(name, bases, dict)
mapping = dict.get('mapping', None)
if mapping:
cls.select_ = cls.select
cls.select = select
class LazyMapper(ActiveMapper):
__metaclass__ = LazyMapperMeta
class SelectResults(object):
def __init__(self, mapper, limit=None, offset=0, *args, **kw):
self.mapper = mapper
self.limit_ = limit
self.offset = offset
self.args = args
self.kw = kw
def __getitem__(self, index):
limit = 1
offset = self.offset + int(index)
return self.mapper.select_(limit=limit, offset=offset,
*self.args, **self.kw)[0]
def __getslice__(self, start, stop):
limit = stop - start
offset = self.offset + start
if limit <= 0:
return []
return SelectResults(self.mapper, offset=offset,
*self.args, **self.kw).limit(limit)
def __iter__(self):
items = self.mapper.select_(limit=self.limit_, offset=self.offset,
*self.args, **self.kw)
for i in items:
yield i
def limit(self, limit):
if self.limit_ and limit > self.limit_:
limit = self.limit_
return SelectResults(self.mapper, limit=limit, offset=self.offset,
*self.args, **self.kw)
